I am interested in having the rear fender marker lights in my 08 450 Dually go on with the light switch, but flash when I hit the turn signals/4ways. I watched a mechanic do it a long time ago (1988) with the front bumper marker poles on my Kenworth, and he said you just have to take a certain wire +or- on the light to a certain wire +or- on the flashing light, and the light will be on with the lights, but flash when the side it is hooked up to flashes, and I can't remember to save my life which it is. Anyone done this mod yet or heard of it?